Add more variation support on Mac.

With the recent transition to creating fonts from data as CTFonts and
dropping variation support from macOS 10.11 and earlier, it is now
possible to reliably make variation clones and get the axis information.

Change-Id: Ia9a0922ac94a29e1508d2e74d4ce973751044866
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/259421
Reviewed-by: Herb Derby <herb@google.com>
Reviewed-by: Dominik Röttsches <drott@chromium.org>
Commit-Queue: Ben Wagner <bungeman@google.com>
3 files changed